Flat panel displays are typically backlit by light guide slabs (often referred to as “backlights”) that provide uniform illumination to a transmissive light valve. The backlight may be the primary light source for the display, or a source of supplemental illumination in a predominantly reflective (often referred to as a “transflective”) display. Alternatively, flat panel reflective displays may be front-lit by a light guide slab (often referred to as a “frontlight” or “front light guide”) that provides uniform illumination from the viewing side of a reflective light valve. This allows elimination of the backlight and placement of a reflector in the light valve, thereby increasing the display's reflectivity and brightness in well-lit ambient light conditions when the frontlight is turned off. Front light guides should have sufficient clarity so that they do not distort or significantly attenuate the display image. Preferably the front light guide also uniformly illuminates the display at a brightness level sufficient to render the display readable in dark ambient conditions.
Displays may also incorporate touch panels that allow the user to input information via a stylus or finger pressure. For example, a common type of touch panel known as a “resistive overlay” design utilizes two transparent layers with partially conductive coatings separated by spacers. When the layers are pressed together, the electrical resistance is sensed in two dimensions to obtain the coordinates of the contact point. The bottom layer (the layer closest to the display) typically is quite stiff and made of glass. The top layer (the layer that will be touched by the stylus or finger) typically is fairly flexible and made of plastic.
Resistive overlay and other touch panel designs are described in the “Carroll Touch Handbook”, available at www.carrolltouch.com. Many such other touch panel designs, including “capacitive overlay”, “guided acoustic wave”, “surface acoustic wave” and “near field imaging” (see U.S. Pat. No. 5,650,597) touch panels, incorporate an optically clear, relatively stiff slab atop the display. Some types of “scanning infrared” touch panels also incorporate an optically clear, relatively stiff slab atop the display. As with resistive overlay designs, glass is most commonly used to form the stiff slab.
Japanese Published Patent application No. JP 11344695A (equivalent to WO 9963394) shows an integral front light guide and touch panel in which the light guide portion is made of molded plastic. The upper surface of the light guide is bonded to the lower surface of the touch panel using a layer of transparent resin, and the lower surface of the light guide has a polygonal or circular dot pattern formed by an ink of transparent or semi-transparent resin having a higher refractive index than the light transmission plate and containing a photodiffusion pigment. Alternatively, the lower surface of the light guide can be formed with “fine crimps” or with “prisms” (shown as sawtooth projections) formed parallel to the end face of the input of the light transmission plate. The light guide of this reference utilizes scattering by the above-mentioned photodiffusion pigment, or refraction through the above-mentioned crimps or prisms, to extract light from the light guide into a light valve. The sawtooth projections in this reference are oriented with the inclined portion of the sawtooth facing away from the light input end of the light guide.
Japanese Published Patent application No. JP 2000-47178A shows an integral front light guide and touch panel in which the light guide portion is wedge-shaped and has a pattern of spacers on its upper surface. The light guide of this reference utilizes scattering by the spacers to extract light from the light guide into a light valve.
Other illuminated touch panel display devices are shown in Japanese Published Patent Application Nos. JP 61188515A, JP 11065764A, JP 11110131A, JP 11174972A, JP 11260133A, JP 11316553A, JP 11065764A and JP 2000075293A, and in PCT Published Patent Application No. WO 99/63394A.
U.S. Pat. No. 5,396,350 shows a backlight having an array of microprisms that reflect light into a transmissive light valve.
U.S. Pat. No. 5,428,468 shows an illumination system employing a waveguide and an array of microprisms that reflect light out of the waveguide. U.S. Pat. No. 5,995,690 shows a light extraction tape for coupling light out of a waveguide.
Other illuminated frontlit or backlit illumination or display devices are shown in U.S. Pat. Nos. 4,373,282; 4,528,617; 4,751,615; 4,799,137; 4,811,507; 4,874,228; 5,005,108; 5,050,946; 5,054,885; 5,190,370; 5,341,231; 5,359,691; 5,485,354; 5,506,929; 5,555,109; 5,555,329; 5,575,549; 5,594,830; 5,608,550; 5,608,837; 5,613,751; 5,668,913; 5,671,994; 5,835,661; 5,894,539; 6,011,602 and 6,139,163; and in European Patent Application EP 0 802 446 A1.